Lock on lets you get your kills faster, so battles are shorter and less likely to be interrupted. I'm not saying your opinion is wrong, but part of what it's based on is.
I get the point, lockon means you can take a guy out more reliably.
I feel like that means anyone could lockon from within range, and snatch the kill. If they were at a far enough distance to where lockon would still work, but playing hardcore, they would have to take a bit to aim.
Then again, if the guy couldn't be taken out quickly enough, in comes the guy with superlegs+ imp. Melee. ....guilty haha >.<
Avoiding the debate regarding lockon, I think some of the other advantages of FFA have to do with the match size.
Frequently 2 v 1 is not fun for anyone, so in smaller matches FFA is definitely better. I would also say that 3 v 2 can be pretty uneven, especially in modes like Power Surge, Annexation, and CTF. I don't mind a 2 v 1 as long as I'm the 1, but if I'm part of the 2, it's pretty boring.
So, unless there are an even number of players, or six or more, FFA is just more enjoyable for me.
Additionally, because you're not restricted to spawning around your own base, there are more possible spawn sites for each player in FFA, which all but eliminates Spawn Camping. Spawn Camping pretty much ruins a team match.
It's true that Team Games let you fall back while someone else covers for you, but I've never really taken advantage of that. I'm just not the fall back type (sorry Chain).